I. Field
The present disclosure relates generally to electronics, and more specifically to amplifiers.
II. Background
Amplifiers are commonly used in various electronics devices to provide signal amplification. Different types of amplifiers are available for different uses. For example, a wireless communication device such as a cellular phone may include a transmitter and a receiver for bi-directional communication. The receiver may utilize a low noise amplifier (LNA), the transmitter may utilize a power amplifier (PA), and the receiver and transmitter may utilize variable gain amplifiers (VGAs).
An LNA is commonly used in a receiver to amplify a low-amplitude signal received via a communication channel. The LNA is often the first active circuit encountered by the received signal and hence has a large impact on the performance of the receiver in several key areas. First, the LNA has a large influence on the overall noise figure of the receiver since the noise of the LNA is injected directly into the received signal and the noise of subsequent circuits is effectively reduced by the gain of the LNA. Second, the linearity of the LNA has a large influence on both the design of subsequent circuits in the receiver and the receiver performance. The LNA input signal typically includes various undesired signal components that may come from external interfering sources and leakage from a co-located transmitter. Nonlinearity of the LNA causes the undesired signal components to mix and generate cross modulation distortion components that may fall within the desired signal bandwidth. The amplitude of the distortion components is determined by the amount of nonlinearity of the LNA. Distortion components that fall within the desired signal bandwidth act as noise that may degrade the signal-to-noise ratio (SNR) of the desired signal, which may in turn degrade performance. Therefore, an LNA having good linearity and low noise figure may be highly desirable.